The present invention relates to a surface emitting type laser array having an "outer" inclined reflecting mirror and employed as a light source for an optical communication, an optical measurement, optical computing, or as a light source for writing information and a latent image into an optical disk and a photosensitive material.
Since the surface emitting type laser element may derive the laser light perpendicular to the semiconductor substrate surface, this laser element can be easily manufactured as a two-dimensional array. The two-dimensional surface emitting type laser array is a very useful element for constituting such systems of parallel optical transmission, coupling between electron integrated circuits, parallel information processing, image processing, and the like.
There are three present-day surface emitting type semiconductor laser elements under development: That is,
(1). the vertical-direction cavity type surface emitting semiconductor laser element; PA1 (2). the surface emitting type semiconductor laser element with combination of the horizontal-direction cavity and the 45-degree inclined reflecting mirror; and PA1 (3). the surface emitting type semiconductor laser element with combination of the horizontal-direction cavity and the distributed brag reflector (DBR).
Among these recently developed surface emitting type semiconductor laser elements, such a surface emitting type semiconductor laser element that both of the semiconductor laser element having the horizontal-direction cavity, and the 45-degree outer inclined reflecting mirror are manufactured on the semiconductor substrate in the monolithic integrated form, is known from the following publications: i.e., Japanese Laid-open Patent Application No. 61-290788 (opened in 1986); Applied Physics Letters, Volume 31, No. 8 (1977), pages 524; Applied Physics Letters, Volume 46, No. 2 (1985), pages 115 to 117; U.S. Pat. Nos. 4,718,070; 4,990465; 4,784,722; and 4,935,939.
FIG.10 is a perspective view for schematically indicating the surface emitting type laser element as described in the above-mentioned Japanese Laid-open Pat. Application No. 61-290788. In this surface emitting type laser element, the semiconductor laser element 35 having the horizontal-direction cavity and the 45-degree outer inclined reflecting mirror 36 are manufactured on the semiconductor substrate in the monolithic form.
Since the surface emitting type semiconductor laser element owns such a feature of high optical output power, as compared with the above-described item (1), i.e., the vertical-direction cavity type surface emitting semiconductor laser element (refer to, e.g., Electronic Communication Institute Technical Research Report OQE 84-9, in 1984), this surface emitting type semiconductor laser element may be utilized not only as a light source for a long distance optical communication, but also as a light source used to write information into an optical disk, and furthermore as a light source for writing a latent image into a photosensitive drum and the like.
In the case that this surface emitting type semiconductor laser element is utilized as a light source for writing a latent image into either an optical disk, or a photosensitive drum and the like, this semiconductor laser element has been used as a multi-beam semiconductor laser element in order to increase writing density, or reducing writing time. That is, as illustrated in FIGS. 11(a) and 11(b), a plurality of stripe electrodes 35 are formed in a parallel manner with each other on the common substrate, the surface emitting type semiconductor laser elements are arranged in an array form on in the semiconductor substrate surface, and also the intervals 37 between the adjoining semiconductor laser elements are made narrow, i.e., several tens of microns.
Such a surface emitting type semiconductor laser element, in which the stripe electrodes 35 are integrated along the same direction in the surface emitting type semiconductor laser element, and also the intervals 37 between the adjoining stripe electrodes are made narrow, i.e., several tens of microns, has several problems.
That is, a first of these problems is crosstalk. Namely, an electric crosstalk problem is produced such that a portion of current injected into a certain semiconductor laser element, is injected into the adjoining semiconductor laser elements, so that optical output power of the adjoining semiconductor laser elements is accidentally increased. Further, a thermal crosstalk problem is produced such that the heat produced while a certain semiconductor laser element is oscillated is transferred to the adjoining semiconductor laser elements, whereby the optical output power of the adjoining semiconductor laser elements is accidentally decreased. These crosstalk problems must be suppressed as much as possible in order to independently drive the multi-beam semiconductor laser element.
A second problem is a manufacturing problem occurring when a large number of bonding pads are fabricated on the multi-beam semiconductor laser element. In a semiconductor laser element, bonding pads electrically connected to stripe electrodes must be formed on a surface of the semiconductor laser element so as to conduct lead wires from the stripe electrodes. As this bonding pad, an area defined by 100.times.100 micrometers, for examples is required. In the normal single beam semiconductor laser element, as indicated in FIGS.12 (a) and 12(b), since only one stripe electrode 40 is formed in the semiconductor laser element 38, there is no problem in forming a bonding pad 39 having an area on the order of 100.times.100 micrometers on the insulating film 41 of the semiconductor laser element 38.
However, when a large number of stripe electrodes positioned in parallel are arranged adjacent to each other in narrow intervals, such as several tens of microns with respect to the multi-beam semiconductor laser element, there is a problem in that the bonding pad 39 having the dimension of 100.times.100 micrometers could not be directly connected to the respective stripe electrode 40, as represented in FIG. 12.
As the means for solving such a latter problem that the area for forming the bonding pad could not be maintained, there are proposed the structures (refer to Japanese Laid-open Pat. Application No. 2-39583 and No. 2-237186), and the multi-layer wiring structure. That is, as shown in FIG.13, the bonding pad 41 is provided apart from the stripe electrode 42, and the bonding pad 41 is connected with the stripe electrode 42 by way of the drawing wiring line 43 on the surface emitting type semiconductor laser element in the first-mentioned structure as described in these Japanese Laid-open Pat. Applications. In the latter multi-layer wiring structure, as illustrated in FIG. 14, the insulating film 46 made of S.sub.i O.sub.2 and the like is formed on the stripe electrode 45, and then the bonding pad 48 of the stripe electrode 47 is fabricated on this insulating film 46.
However, since the drawing wiring line 43 intersects the upper portion of the active region 44 extending on the outer stripe in the structure shown in FIG.13, the depletion region is varied, which is formed in the active region 44 in response to the voltage applied to this drawing wiring line 43, is varied. Accordingly, the profile of current injected into the active layer is changed, so that there is the inconvenience that the optical output power is varied. Also, the structure indicated in FIG. 14 has not only such a drawback that the manufacturing process becomes complex and also the number of processing stage is considerably increased, but also, problem that since the insulating film such as S.sub.i O.sub.2 is laminated on G.sub.a A.sub.s whose thermal expansion coefficient is different from that of this insulating film, stress is applied to the semiconductor laser element longitudinal structure containing G.sub.a A.sub.s while the electrode is thermally processed, thereby including an occurrence of transition or dislocation, resulting in damage of the resultant device.
On the other hand, as the method for manufacturing the reflecting surface of the external inclined reflecting mirror, there are proposed: the method for manufacturing the 45-degree reflecting surface with employment of the wet etching (refer to "Continuous Oscillation of BTRS type GaAlAs Semiconductor Laser having Cavity Edge Surface by Chemical Etching in Room, Temperature" by Shibuya et al., Electronic Communication Institute Technical Research Report ED84-95, 1984, pages 75 to 81); and the masstransport method with combination of the wet etching and the annealing (refer to "Surface-emitting GaInAsP/InP Laser with Low Threshold Current and High Efficiency" by Z. L. Lian et al., Applied Physics Letter, Vol. 46, No. 2, 1985, page 115).
The former method for manufacturing the 45-degree reflecting surface with employment of the wet etching owns such a restriction that the stripe extending direction of the surface emitting type semiconductor laser element is limited only to the direction of &lt;0 1 1&gt;, because the 45-degree reflecting surface is fabricated by utilizing that the etched angle of AlGaAs owns the surface azimuth depending characteristic. When the reflecting surface is manufactured by the latter mass transport method, since the laser edge surface positioned opposite to this reflecting surface is cut at the right angle with respect to the plane (100) of the semiconductor substrate, there is a restriction such that the stripe extending direction of the surface emitting type semiconductor laser element is directed only to the direction of &lt;0 1 1&gt;.
Due to the above-described reasons, the above-explained methods described in the publications have such a problem that the surface emitting type semiconductor laser element cannot be freely arranged on the semiconductor substrate.